TTGWD1-25 牛牛们来帮忙

sasha_wen · 发表于 2009-12-28 15:24:40

A photographer will arrange 6 people of 6 different heights for photograph by placing them in two rows of three so that each person in the first row is standing in front of someone in the second row. The heights of the people within each row must increase from left to right, and each person in the second row must be taller than the person standing in front of him or her. How many such arrangements of the 6 people are possible?

A. 5

B. 6

C. 9

D. 24

E. 36

答案是A，请教牛牛怎么做？

vivian7765 · 发表于 2009-12-28 16:13:21

设6个人是1.2.3.4.5.6，分别的从低到高。前排的排法分别有123，124，125，134，135.分别对应的后排顺序是456，356，346，256，246.。所以一共是五种

sasha_wen · 发表于 2009-12-28 18:56:48

谢谢楼上的牛牛。

有没有不用这样凑的方法，直接用乘法原理和加法原理解题的

TTGWD1-25 牛牛们来帮忙

所属分类: GMAT考试

正在浏览此版块的会员 ()